The present invention relates to apparatus for processing a composite video signal substantially all the lines of which each comprise a line synchronising pulse, a front and a back porch and a vision portion, said apparatus comprising an input terminal for receiving said composite video signal, a first signal path having its input connected to said input terminal which first signal path includes first enabling means for enabling said first signal path outside the period of the synchronising pulse in each line period.
Such apparatus may be used in players for optically recorded video discs such as Laservision or CD Video (Compact Disc Video) where the synchronising pulses for PAL video signals contain a burst of pulsed additional information, called the video signal pilot burst, at a frequency of 3.75 MHz which is used for time base error correction. Apparatus of the type described in the opening paragraph is disclosed in Japanese Kokai No. 58-119287 which provides a vision signal path including an eliminating circuit which conveys the vision signal outside the line synchronising pulse periods, these synchronising pulses containing pilot burst. The nature of this pilot burst is given in the IEC standard UAR-2516-596/8412 Pre-recorded optical reflective video-disk system "Laservision" 50 Hz/625 lines - PAL, first edition 1984. Such a special burst is not required with NTSC video signals recorded on such discs as the relationship of the frequency of the colour burst to that of the line frequency (227.5 times) is such that the colour burst can be used for such time base error correction. However, this is not possible with PAL video signals recorded on such discs due to the offset in the colour burst-to-line frequency relationship and the change in phase of the burst from line to line. It is for this reason that the pilot burst is added to the PAL signal. As an alternative such apparatus may be used where a burst of pulsed additional information in the synchronising pulses contains audio (sound in syncs) or other information or where it is desired to replace the synchronising pulses with a reference level. In either case when processing the composite video signal the burst in the synchronising pulse can cause problems such as when trying to synchronise the video signal.